A known variable valve timing control apparatus controlling a relative rotation phase of a driven-side rotation member relative to a driving-side rotation member that rotates in synchronization with a crankshaft of an internal combustion engine may change an opening and closing timing of an intake valve and an exhaust valve depending on an operation condition of the internal combustion engine. Such variable valve timing control apparatus includes a mechanism for changing the opening and closing timing of the intake valve and the exhaust valve that open and close in association with the rotation of the driven-side rotation member by changing a relative rotation phase of the driven-side rotation member relative to the driving-side rotation member that rotates by an operation of the engine.
Generally, an optimum opening and closing timing of the intake valve and the exhaust valve depends on an engine operation condition at an engine start and driving of a vehicle, for example. Thus, at the engine start, the relative rotation phase of the driven-side rotation member relative to the driving-side rotation member is locked at a predetermined phase between a most retarded angle phase and a most advanced angle phase. As a result, the optimum opening and closing timing of the intake valve and the exhaust valve for the engine start is achieved and a generation of hitting sound by rotation or movement of a partition portion provided at a hydraulic chamber that is formed by the driving-side rotation member and the driven-side rotation member is restrained. It is thus desirable to lock the relative rotation phase at the aforementioned predetermined phase before the engine is stopped.
JP2004-257313A, which will be hereinafter referred to as Reference 1, discloses a variable valve timing control apparatus that includes two lock members (moving members) and two recess portions (grooves) fitted to the respective lock members so that the relative rotation phase is locked at an intermediate lock phase between the most advanced angle phase and the most retarded angle phase. In the variable valve timing control apparatus disclosed in Reference 1, one of the lock members, i.e., an advanced angle lock portion, restricts the relative rotation phase from changing to a retarded angle direction while the other of the lock members, i.e., a retarded angle lock portion, restricts the relative rotation phase from changing to an advanced angle direction. Each of the recess portions is formed with a ratchet, i.e., a stepped portion. In a case where the relative rotation phase changes from the most retarded angle phase to the intermediate lock phase, the two lock members are alternately fitted to the corresponding ratchets and then alternately fitted to the corresponding recess portions so as to restrict the relative rotation phase from changing in an opposite direction. The relative rotation phase may be securely locked at the intermediate lock phase accordingly.
JP2009-250073A, which will be hereinafter referred to as Reference 2, discloses a variable valve timing control apparatus (a valve timing adjusting apparatus) including one lock member (a lock pin) and one restriction member (a restriction pin). The lock member is configured to be fitted to a lock recess portion (a lock bore) while the restriction member is configured to be fitted to a restriction recess portion (restriction groove). In the variable valve timing control apparatus disclosed in Reference 2, the lock member is fitted to the lock recess portion to lock the relative rotation phase at the intermediate lock phase between the most advanced angle phase and the most retarded angle phase to simultaneously restrict the relative rotation phase from changing to the advanced angle direction and the retarded angle direction. A ratchet (a limiting groove) is formed at the lock recess portion. Each of the lock member and the restriction member includes a body portion and a projection portion that are formed by an outer peripheral surface in a stepped cylindrical form, the diameter of the outer peripheral surface decreasing in a stepped manner in a fitting direction of the lock member and the restriction member relative to the lock recess portion and the restriction recess portion. In the aforementioned configuration, in a case where the relative rotation phase changes from the most retarded angle phase to the intermediate lock phase, the projection portion and the body portion of the lock member are sequentially fitted to the ratchet, and then the projection portion and the body portion of the restriction member are sequentially fitted to the restriction recess portion. Thereafter, the projection portion and the body portion of the lock member are sequentially fitted to the lock recess portion. Accordingly, the relative rotation phase is restricted from changing in an opposite direction to thereby securely lock the relative rotation phase at the intermediate lock phase.
JP2010-138699A, which will be hereinafter referred to as Reference 3, discloses a variable valve timing control apparatus (a valve timing control apparatus) in which two lock members (lock pins) are fitted to two recess portions (lock holes) respectively to lock the relative rotation phase at the intermediate lock phase between the most advanced angle phase and the most retarded angle phase. In the variable valve timing control apparatus disclosed in Reference 3, in a case where a lock request is generated, an engine control circuit performs a phase variable control. During the phase variable control, in a case where an actual camshaft phase (an actual valve timing of the intake valve) does not move in the vicinity of the intermediate lock phase, the engine control circuit changes a control duty of a hydraulic control valve for a phase control by a predetermined amount so as to further move the actual camshaft phase. When the actual camshaft phase still does not move, it is determined that locking of the relative rotation phase is completed. It may be securely detected that the relative rotation phase is locked at the intermediate lock phase. Here, the actual camshaft phase is synonymous with the relative rotation phase. The actual camshaft phase is calculated by the engine control circuit based on detection signals of a cam angle sensor and a crank angle sensor.
In order to restrain a hitting sound caused by rotation or movement of the partition portion at the hydraulic chamber that is formed by the driving-side rotation member and the driven-side rotation member, a gap (clearance) formed between the lock member and the recess portion in a locked state at the intermediate lock phase is necessarily small. In order to reduce the aforementioned gap, dimensional accuracy of the lock member and the recess portion is necessarily increased. Nevertheless, the increase of dimensional accuracy may lead to cost increase at a time of mass production. In a case where the gap between the lock member and the recess portion is small, accuracy for positioning the lock member and the recess portion at the intermediate lock phase is necessarily increased when he relative rotation phase is shifted so that the locked state is established from an unlocked state. Certain time is required for obtaining the locked state to thereby disturb a prompt operation of the variable valve timing control apparatus.
The variable valve timing control apparatus disclosed in Reference 1 includes the two lock members and the two recess portions. One of the lock members is fitted to one of the recess portions to restrict the relative rotation in the advanced angle direction. The other of the lock members is fitted to the other of the recess portions to restrict the relative rotation in the advanced angle direction. Thus, in order to reduce the gap formed between each of the lock members and each of the recess portions in the locked state of the relative rotation, in addition to increasing accuracy of length dimensions of the lock members and the recess portions, angle dimensions between the two lock members and between the two recess portions are necessarily increased. Nevertheless, in order to achieve the fitting of two lock members relative to the two recess portions at the same time in the mass production, the number of dimensions on which accuracy control should be conducted is large. Thus, when considering dimension variations of components under the mass production, it is difficult to increase accuracy. Therefore, in practical, the gap between the lock member and the recess portion may be inhibited from being reduced and hitting sound may be inhibited from being restrained.
In the variable valve timing control apparatus disclosed in Reference 2, the single lock member is fitted to the single lock recess portion to lock the relative rotation phase at the intermediate lock phase. Thus, as compared to the variable valve timing control apparatus in Reference 1, the number of dimensions on which accuracy control is necessary is small, which may achieve a smaller gap between the lock member and the lock recess portion in the locked state of the relative rotation. Nevertheless, in a case where the relative rotation phase changes at a high speed to the intermediate lock phase in a state where the gap between the lock member and the recess portion is small and the relative rotation phase is in the vicinity of the most advanced angle phase, the lock member may pass over the intermediate lock phase without being fitted to the lock recess portion. A wrong operation may occur so that the lock member hits a wall of the ratchet and stops. In such case, in order to obtain the locked state, the aforementioned wrong operation in which the lock member has passed over the intermediate lock phase should be detected by a sensor, and the relative rotation phase should be shifted in an opposite direction based on a detection result by the sensor to obtain the locked state. At this time, it requires time for achieving the locked state, thereby disturbing the prompt operation of the variable valve timing control apparatus.
In the variable valve timing control apparatus disclosed in Reference 3, in a case where the lock request is made, the engine control circuit performs the phase variable control. In a case where the actual camshaft phase does not move in the vicinity of the intermediate lock phase during the control by the engine control circuit, the engine control circuit further changes the control duty of the hydraulic valve for the phase control so that the actual shaft phase moves by the predetermined amount. At a time when the lock request is made, the actual camshaft phase is not arranged at the intermediate lock phase. Thus, the engine control circuit controls the control duty of the hydraulic valve for the phase control to change so that the actual shaft phase moves towards a phase beyond the intermediate lock phase. According to the aforementioned control, the lock member may not surely fitted to the recess portion to achieve the locked state during the phase change and the locked state may not be obtained as the lock member passes over the recess portion. In a case where the engine control circuit determines that the actual camshaft phase has passed over the intermediate lock phase, the change direction of the actual camshaft phase is reversed and the actual camshaft phase is controlled towards the phase beyond the intermediate lock phase. The aforementioned series of control is repeated until the relative rotation phase is locked at the intermediate lock phase. The aforementioned state in which the actual camshaft phase does not move in the vicinity of the intermediate lock phase corresponds to the locked state at the intermediate lock phase, and also indicates a state where the intermediate lock phase is changeable by an amount corresponding to the gap between the lock member and the recess portion. In a case where the control duty of the hydraulic control valve for the phase control is further shifted by the predetermined amount in the direction to move the actual camshaft phase in the state where the actual camshaft phase does not move in the vicinity of the intermediate lock phase, and the actual camshaft phase is not changed from the vicinity of the intermediate lock phase, the engine control circuit determines that the actual camshaft phase is arranged at the intermediate lock phase and the locked state is achieved. Accordingly, the variable valve timing control apparatus in Reference 3 is intended to confirm whether the locked state is established after the actual camshaft phase is locked at the intermediate lock phase.
The engine control circuit is required to accurately calculate or determine that the actual camshaft phase is in the vicinity of the intermediate lock phase or beyond the intermediate lock phase, for example, i.e., to accurately calculate an actual value of the actual camshaft phase. Thus, the cam angle sensor and the crank angle sensor necessarily accurately detect a cam angle and a crank angle to output detection signals respectively. In addition, a difference in output timing of the respective detection signals by the cam angle sensor and the crank angle sensor is necessarily accurate. At this time, a difference may occur between the actual value of the actual camshaft phase and the calculated actual camshaft phase based on the cam angle sensor and the crank angle sensor, i.e., a detection error may occur. When the detection error occurs, the engine control circuit determines that the relative rotation is positioned at the intermediate lock phase though the relative rotation is not actually positioned at the intermediate lock phase and performs a locking confirmation operation, or determines that the relative rotation is not positioned at the intermediate lock phase though the relative rotation is actually positioned at the intermediate lock phase and reverses the change direction of the actual camshaft phase, for example, which may cause a wrong operation.
A need thus exists for a variable valve timing control apparatus which is not susceptible to the drawback mentioned above.